1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor device to which magnetic domain wall movement is applied.
2. Description of the Related Art
Data storing devices are divided, for the most part, into volatile data storing devices that lose all recorded data when power is turned off and non-volatile data storing devices that keep data even when power is turned off.
Non-volatile data storing devices include a hard disc drive (HDD) and a non-volatile random access memory (RAM). The HDD includes a read and write head and a rotating data recording medium, and can store data of 100 gigabytes or more. However, a device that has a rotating part like the HDD has a problem in that it wears down over time, and thus, there is a high possibility of operational failure, thereby reducing reliability.
A flash memory which is widely used is an example of non-volatile RAM. However, the flash memory has drawbacks of slow reading and writing speeds and short life span. Due to the drawbacks of the flash memory, new memory devices such as ferroelectric random access memory (FRAM), magnetic random access memory (MRAM), and phase change random access memory (PRAM) have been developed. However, the flash memory, FRAM, MRAM, and PRAM all have small storage capacities when compared to a HDD and have high manufacturing costs.
Therefore, as a method of solving the drawbacks of the conventional non-volatile data storing devices as described above, much research and development with respect to a new data storing device that uses a magnetic domain wall movement has been carried out.
A magnetic domain in a magnetic substance and magnetic domain walls will now be described. Afterwards, a storing device that uses the magnetic domain and the magnetic domain walls will be described.
A minute magnetic region that constitutes a ferromagnetic body is named as a magnetic domain. The rotation of electrons in a magnetic domain, that is, the direction of magnetic moment is identical. The size and magnetization direction of a magnetic domain can be appropriately controlled by the shape and size of a magnetic substance and external energy.
A magnetic domain wall is a boundary portion of a magnetic domain having a magnetization direction different from another magnetic domain. The magnetic domain wall can be moved by an external magnetic field or by a current applied to a magnetic substance.
The principle of the magnetic domain wall movement can be applied to data storing devices such as HDDs. That is, an operation of reading/writing data is possible when the magnetic domains magnetized so as to correspond to specific data in a magnetic substance are moved in order to pass through a read/write head. In this case, a reading/writing operation is possible without directly rotating a recording medium. Accordingly, the problems of wearing down and failure of conventional HDDs can be solved. An example of a data storing device to which the principle of magnetic domain wall movement is applied has been disclosed in U.S. Pat. No. 6,834,005 B1.
Also, the principle of magnetic domain wall movement can be applied to a memory such as a non-volatile RAM. That is, a non-volatile memory device that can write/read a data ‘0’ or ‘1’ can be realized using a principle whereby a voltage in a magnetic substance varies according to the movement of magnetic domain walls in the magnetic substance having magnetic domains magnetized in a specific direction and magnetic domain walls. In this way, since data can be read and written by varying the positions of the magnetic domain walls by flowing a specific current in a line type magnetic substance, a highly integrated device having a simple structure can be realized. Therefore, when the principle of magnetic domain wall movement is used, the manufacture of a memory having a very large storage capacity compared to the conventional FRAM, MRAM, and PRAM is possible.
However, the development of semiconductor devices that use the magnetic domain wall movement is still in an initial stage, and there are a few problems that have yet to be solved in order for them to be used in practice. One of the problems is related to the mobility of the magnetic domain walls. If the movement of the magnetic domain walls is slow, a sufficient speed of reading/writing cannot be achieved. The magnetic domain walls in a magnetic substance must be able to stably move at a high speed in a magnetic field or when a current is applied. However, a physical phenomenon in relation to the speed of movement of the magnetic domain walls has not yet been theoretically clearly identified. Therefore, there is a difficulty in improving the speed of movement of the magnetic domain walls.